Cranial neural crest cells, which contribute to the formation of many craniofacal structures, differentiate in culture into two of their normal derivatives, neurons and pigment cells. As an approach toward defining the factors which affect normal and abnormal neural crest development, we are examining various aspects of their differentiation in culture. The well-defined and reproducible differentiation of neural crest cultures has enabled us to develop a system to screen for teratogens in vitro.